Continuous transformation of decagonal quasicrystal to a related crystalline phase

1990 ◽  
Vol 48 (4) ◽  
pp. 132-133
Author(s):  
K.H. Kuo ◽  
H. Zhang
Keyword(s):  
Electron Diffraction ◽  
Rotation Axis ◽  
Orthorhombic Phase ◽  
Structural Similarity ◽  
Two Dimensional ◽  
Continuous Transformation ◽  
Decagonal Quasicrystal ◽  
Decagonal Phase ◽  
Selected Area Electron Diffraction ◽  
Rapidly Solidified

Decagonal quasicrystal is a two-dimensional one with a periodicity of about 1.2 or 1.6 nm along its tenfold rotation axis. It is known to exist in rapidly solidified Al-rich Al-Mn-Si and Al-Cr-Si alloys, sometimes coexisting with the bcc α-AlMnSi or cubic Al13Cr4Si4 phase. Both these two crystalline phases are known to have many icosahedral units in them. The structural similarity between the decagonal phase and the related bcc α-AlMnSi has been studied extensively lately.However, recently we have found a new base-centered orthorhombic phase with a=1.24, b=3.79, and c=1.23 nm coexisting with the decagonal phase to these alloys. Moreover, evidence of a continuous transformation from the latter to the former has been found by selected area electron diffraction. Fig. la is the tenfold electron diffraction pattern (EDP) of the decagonal quasicrystal with strong spots forming a series of concentric decagons. However, in the region close to the boundary to the crystal, the circle on which the inner 10 strong spots lie becomes an ellipse with its long axis in the arrowed direction (Fig. 1b). The closer to the boundary, the more the distortion of this decagon (Fig. 1c) and finally the EDP changes almost to a 2D crossgrid pattern of a base-centered crystal (a reciprocal unit cell is outlined in Fig. 1d).

A Metastable Crystalline Phase Coexisted with the Decagonal Quasicrystals in Rapidly Solidified Al-Ir Al-Pd and Al-Pt Alloys

1990 ◽  
Vol 48 (1) ◽  
pp. 572-573
Author(s):  
Wang Rong ◽  
Ma Lina ◽  
K.H. Kuo
Keyword(s):  
Metastable Phase ◽  
Hexagonal Phase ◽  
Icosahedral Quasicrystal ◽  
Decagonal Quasicrystal ◽  
Decagonal Phase ◽  
Decagonal Quasicrystals ◽  
Pt Alloy ◽  
Pt Alloys ◽  
Diffraction Patterns ◽  
Rapidly Solidified

Up to now, decagonal quasicrystals have been found in the alloys of whole Al-Pt group metals [1,2]. The present paper is concerned with the TEM study of a hitherto unreported hexagonal phase in rapidly solidified Al-Ir, Al-Pd and Al-Pt alloys.The ribbons of Al5Ir, Al5Pd and Al5Pt were obtained by spun-quenching. Specimens cut from the ribbons were ion thinned and examined in a JEM 100CX electron microscope. In both rapidly solidified Al5Ir and Al5Pd alloys, the decagonal quasicrystal, with rosette or dendritic morphologies can be easily identified by its electron diffraction patterns(EDPs). The EDPs of the decagonal phase for the two alloys are quite similar. However, the existance of decagonal quasicrystal in the Al-Pt alloy has not been verified by our TEM study. It is probably for the reason that the cooling rate is not great enough for the Al5Pt alloy to form the decagonal phase. During the TEM study, a metastable hexagonal phase has been observed in the Al5Ir, Al5Pd and Al5Pt alloys. The lattic parameters calculated from the X-ray powder data of this phase are a=1.229 and c=2.647nm(Al-Pd) and a=1.231 and c=2.623nm(Al-Ir). The composition of this phase was determined by EDS analysis as Al4(Ir, Pd or Pt). It coexists with the decagonal phase in the alloys and transformed to other stable crystalline phases on heating to high temperature. A comparison between the EDPs of the hexagonal and the decagonal phase are shown in Fig.l. Fig. 1(a) is the EDPs of the decagonal phase in various orientions and the EDPs of the hexagonal phase are shown in Fig.1(b), in a similar arrangement as Fig.1(a). It can be clearly seen that the EDPs of the hexagonal phase, especially the distribution of strong spots, are quite similar to their partners of the decagonal quasicrystal in Fig.1(a). All the angles, shown in Fig.l, between two corresponding EDPs are very close to each other. All of these seem strongly to point out that a close structural relationshipexists between these two phases:[110]//d10 [001]//d2(D) //d2 (P)The structure of α-AlFeSi is well known [3] and the 54-atom Mackay icosahedron with double icosahedral shells in the α-AlFeSi structure [4] have been used to model the icosahedral quasicrystal structure. Fig.2(a) and (b) show, respectively, the [110] and [001] projections of the crystal structure of α- AlFeSi, and decagon-pentagons can easily be identified in the former and hexagons in the latter. In addition, the optical transforms of these projections show clearly decagons and hexagons of strong spots, quite similar to those in [110] and [001] EDPs in Fig.1(b). This not only proves the Al(Ir, Pt, Pd) metastable phase being icostructural with the α-AlFeSi phase but also explains the orientation relationship mentioned above.

Approximants to the icosahedral and decagonal phases in the Al–Cu–Cr system

1991 ◽  
Vol 6 (8) ◽  
pp. 1641-1649 ◽  
Author(s):  
S. Ebalard ◽  
F. Spaepen
Keyword(s):  
Electron Diffraction ◽  
Icosahedral Phase ◽  
Lattice Parameters ◽  
Cubic Phase ◽  
Decagonal Phase ◽  
Bcc Lattice ◽  
Selected Area Electron Diffraction ◽  
Phase Ordering ◽  
Cr System

A 1/1-type approximant to the AlCuCr icosahedral phase and approximants to a decagonal phase have been found in an as-cast Al65Cu20Cr15 ingot. Selected area electron diffraction indicates that the 1/1-type approximant consists of Mackay icosahedra arranged on a bcc lattice, similar to the α-AlMnSi cubic phase. Ordering of the glue atoms produces a base-centered orthorhombic superstructure, making the overall structure monoclinic P2/m, with lattice parameters a = 12.6 Å, c = 17.92 Å, and α = 90°.

Transmission electron microscope observations of rectangular dislocation networks in an Al70Co15Ni15 decagonal quasicrystal

1993 ◽  
Vol 8 (2) ◽  
pp. 286-290 ◽  
Author(s):  
Yanfa Yan ◽  
Renhui Wang
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Transmission Electron Microscope ◽  
The Other ◽  
Dislocation Network ◽  
Decagonal Quasicrystal ◽  
Twofold Axis ◽  
Decagonal Phase ◽  
Diffraction Contrast ◽  
Transmission Electron

The electron diffraction contrast of two types of rectangular dislocation networks in an Al70Co15Ni15 decagonal quasicrystal has been analyzed. One type of dislocation network consists of two dislocation sets whose Burgers vectors are parallel to the tenfold axis A10 and a twofold axis A2D. The other type of dislocation network consists of two dislocation sets whose Burgers vectors are parallel to the A10 and the other twofold axis of A2P. The characteristics of the diffraction contrast of the dislocation networks in the Al–Co–Ni decagonal phase are similar to those in conventional crystals.

Accurate lattice-parameter determination from electron diffraction tomography data using two-dimensional diffraction vectors

2018 ◽  
Vol 51 (4) ◽  
pp. 982-989 ◽  
Author(s):  
Jonas Ångström ◽  
Hong Chen ◽  
Wei Wan
Keyword(s):  
Electron Diffraction ◽  
Rotation Axis ◽  
Three Dimensional ◽  
Lattice Parameter ◽  
Parameter Determination ◽  
Data Sets ◽  
Diffraction Tomography ◽  
Two Dimensional ◽  
Lower Accuracy ◽  
Diffraction Patterns

Electron diffraction tomography (EDT) has emerged as a successful tool for ab initio atomic structure determination of nanometre-sized crystals. However, lattice parameters obtained from EDT data are often of lower accuracy than those from powder X-ray data, owing to experimental errors and data-processing methods. This work describes a lattice-parameter refinement method for EDT data using two-dimensional diffraction vectors and shows that the accuracy of lattice-parameter determination can be improved significantly. It is also shown that the method is tolerant to sample displacement during data collection and to geometric distortions in the electron diffraction patterns due to lens imperfections. For the data sets tested, the method reduces the 95% confidence interval of the worst errors in angles from ±1.98 to ±0.82° and the worst relative errors of the unit-cell lengths from ±1.8% to ±1.3%, compared with the conventional method using clustering of three-dimensional diffraction vectors. The improvement is attributed to the fact that the new method makes use of the positions of two-dimensional diffraction spots, which can be determined with high accuracy, and disregards the position of the central beam, the orientation of the rotation axis and the angles of the diffraction frames, whose errors all contribute to the errors for lattice-parameter determination using the three-dimensional method.

Ordered γ-brass structures coexisting with the decagonal quasicrystal in a Ga46Fe23Cu23Si8 alloy

1999 ◽  
Vol 14 (7) ◽  
pp. 2799-2805 ◽  
Author(s):  
S. P. Ge ◽  
K. H. Kuo
Keyword(s):  
Electron Diffraction ◽  
Orientation Relationship ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Decagonal Quasicrystal ◽  
Parallel Orientation ◽  
Fundamental Structure ◽  
Lattice Correspondence ◽  
Face Centered ◽  
Rapidly Solidified

In a moderately rapidly solidified Ga46Fe23Cu23Si8 alloy, a face-centered-cubic (fcc) superstructure (a = 1.78 nm) and a hexagonal superstructure (ahex = 2.18 nm and chex = 0.77 nm), based on the same body-centered-cubic (bcc) γ-brass structure (a = 0.89 nm), were found—by means of micro-area electron diffraction—to coexist with the decagonal quasicrystal. The fcc superstructure is probably similar to one of the F-centered-γ-brass structure and has a parallel orientation relationship with the bcc fundamental structure. The hexagonal superstructure has its (001) parallel to the (111) of the bcc γ-brass structure and its chex = abcc[111]/2, and their lattice correspondence relationship has been derived. Electron diffraction evidence is presented to show that these two superstructures are possibly crystalline approximants of the decagonal quasicrystal.

Transformation of Al–Ni–(Si) decagonal quasicrystals to 1–D quasicrystal and crystalline approximants

1993 ◽  
Vol 8 (10) ◽  
pp. 2499-2503 ◽  
Author(s):  
X.Z. Li ◽  
K.H. Kuo
Keyword(s):  
Electron Microscopy ◽  
Crystalline Phase ◽  
Two Dimensional ◽  
Decagonal Quasicrystal ◽  
One Dimensional ◽  
Decagonal Phase ◽  
Decagonal Quasicrystals ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Orientational Relationship

Rapidly quenched Al86-xNi14Six (x = 0, 2, 6, and 10) alloys have been studied by means of transmission electron microscopy. Two-dimensional (2-D) decagonal quasicrystal with a periodicity of 1.6 nm along its tenfold axis was found in the rapidly quenched Al86Ni14 binary alloy. With the addition of some silicon, such as AlgoNi14Si6, the 2-D decagonal quasicrystal first transforms to a one-dimensional (1-D) quasicrystal that inherits the periodicity along the tenfold axis and has, in addition, translation periodicity in one of the twofold axes of the decagonal phase, and finally transforms to a new orthorhombic crystalline phase (a = 0.78, b = 1.62, and c = 1.48 nm). In the Al76Ni14Si10 ternary alloy, a 2-D decagonal quasicrystal with a periodicity of 0.4 nm and a coexisting crystalline phase with the “Al3Ni2” structure were found, and their orientational relationship has been determined.

Phase Microidentification from Selected Area Electron Diffraction (SAED) and Energy Dispersive Spectroscopy (EDS) Data

1991 ◽  
Vol 35 (A) ◽  
pp. 687-691 ◽  
Author(s):  
Josef Macicek
Keyword(s):  
Electron Diffraction ◽  
Energy Dispersive Spectroscopy ◽  
Reciprocal Lattice ◽  
Energy Dispersive ◽  
Phase Identification ◽  
Two Dimensional ◽  
Selected Area Electron Diffraction ◽  
Elemental Data

AbstractTwo-dimensional geometry information contained in SAED spot patterns augmented with EDS elemental data is employed in a computerized phase identification of microcrystalline particles. The initial chemistry screening of a laboratory managed database using the 'bitmap' concept is followed by a geometry search/match treating of the spot patterns as planar sections through the reciprocal lattice of a candidate phase. The identification is selective, fast, and yields to a complete automatization,

Quasicrystals with 1-D Translational Periodicity and A Ten-Fold Rotation Axis

1985 ◽  
Vol 58 ◽  
Author(s):  
L. Bendersky
Keyword(s):  
Composition Range ◽  
Intermediate Phase ◽  
Rotation Axis ◽  
Orientational Order ◽  
Point Group ◽  
Icosahedral Phase ◽  
Solidification Condition ◽  
Decagonal Phase ◽  
Points Of View ◽  
Rapidly Solidified

ABSTRACTStudies of phase formation in rapidly solidified Al-Mn alloys (composition range 18-22 at% Mn) show that an icosahedral phase is replaced by another noncrystallographic phase, a decagonal phase. The decagonal phase is another example of quasicrystal: It has a noncrystallographic point group (10/m or lO/mmm) together with long-range orientational order and onedimensional translational symmetry. The decagonal phase is an intermediate phase between an icosahedral phase and a crystal both from the symmetry and from the solidification condition points of view.

Pollutant Identification by Selected Area Electron Diffraction

1974 ◽  
Vol 32 ◽  
pp. 532-533
Author(s):  
R. E. Ferrell ◽  
G. G. Paulson ◽  
C. W. Walker
Keyword(s):  
Thermal Treatment ◽  
Electron Diffraction ◽  
Sample Preparation ◽  
Crystal Structures ◽  
Water Samples ◽  
Environmental Samples ◽  
Short Review ◽  
Selected Area Electron Diffraction ◽  
Multiple Component

Selected area electron diffraction (SAD) has been used successfully to determine crystal structures, identify traces of minerals in rocks, and characterize the phases formed during thermal treatment of micron-sized particles. There is an increased interest in the method because it has the potential capability of identifying micron-sized pollutants in air and water samples. This paper is a short review of the theory behind SAD and a discussion of the sample preparation employed for the analysis of multiple component environmental samples.

Bimolecular and Monomolecular Lipid Films: Selected Area Electron Diffraction

1969 ◽  
Vol 27 ◽  
pp. 338-339
Author(s):  
Robert M. Glaeser ◽  
David W. Deamer
Keyword(s):  
Electron Diffraction ◽  
Membrane Structure ◽  
Molecular Organization ◽  
Membrane Material ◽  
X Ray Diffraction ◽  
Membrane Systems ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Lipid Films ◽  
Ultimate Objective

In the investigation of the molecular organization of cell membranes it is often supposed that lipid molecules are arranged in a bimolecular film. X-ray diffraction data obtained in a direction perpendicular to the plane of suitably layered membrane systems have generally been interpreted in accord with such a model of the membrane structure. The present studies were begun in order to determine whether selected area electron diffraction would provide a tool of sufficient sensitivity to permit investigation of the degree of intermolecular order within lipid films. The ultimate objective would then be to apply the method to single fragments of cell membrane material in order to obtain data complementary to the transverse data obtainable by x-ray diffraction.

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